1. Field of the Invention
The present invention relates to an ink jet head drive circuit and an ink jet recording apparatus, and more particularly to an ink jet head drive circuit and an ink jet recording apparatus capable of increasing a monochrome print speed without causing an ink supply shortage to an output image.
2. Discussion of the Background
Generally, when compared with printing devices such as dot matrix impact printers, etc., an ink jet recording apparatus produces substantially small amounts of vibrations and acoustic noises during its recording operations and is suitable for an application of color printing. This is a major reason that the ink jet recording apparatus has widely been adopted for use in various printing applications such as in a printer, a facsimile apparatus, a copying apparatus, and so forth.
The background ink jet recording apparatus is generally provided with a recording head unit that includes an ink cartridge and an ink jet head. The ink jet head includes a plurality of nozzles for discharging ink and a corresponding plurality of actuating elements, such as piezoelectric elements, exothermic reaction resisting elements, or so forth. The plurality of actuating elements provided inside the ink jet head are selectively driven with a signal that represents an image, so that a desired amount of ink can be discharged from the ink cartridge through the nozzles and fall onto a recording medium. In this way, the ink jet recording apparatus produces an output image on a recording medium.
The above-mentioned ink jet recording apparatus has lately been required to perform printing operations faster than ever. To respond to this requirement, techniques for driving the ink jet head at a high frequency have been developed, so that the ink jet recording apparatus can perform the printing operations faster than ever.
However, the characteristics of the ink discharge of an ink jet head may exert an effect on print quality. More specifically, one of the characteristics of the ink jet head is that an amount of ink to be discharged relates to a stability of an ink surface around the ink discharge orifice and the amount of ink discharged decreases when vibrations are caused on the ink surface. Since vibrations of the ink surface increase with an increasing head drive frequency, the ink discharging amount decreases when the head drive frequency is increased. When the ink discharging amount is decreased, the ink jet recording apparatus may produce an output image having a so-called white line problem which occurs, for example, due to a shortage in the amount of ink discharged. The ink jet head also has another characteristic such that the ink discharging amount relates to a viscosity of the ink and the ink discharging amount decreases when a viscosity of the ink is increased. Since viscosity of ink is increased when a temperature around the ink jet head is decreased, the ink discharging amount is decreased with decreasing temperature around the ink jet head. In this case, the ink jet recording apparatus may also produce the above-mentioned white line problem.
Japanese Laid-Open Patent Application No. 55-27210 discloses an ink jet recording apparatus which changes a voltage level of an ink jet head drive pulse according to environmental temperature.
Also, Japanese Laid-Open Patent Application No. 63-260452 discloses a liquid discharge type recording apparatus which varies a fall time of an ink jet head drive pulse according to an environmental temperature.
However, as the head drive frequency of the background ink jet recording apparatus increases, a reduction curve of ink discharging amount may become steeper to such an extent that compensating according to the environmental temperature is not sufficient.
In addition, the ink jet recording apparatus is often provided with a so-called draft print mode in which an output image is produced in a time faster than that in a regular print mode. In the draft print mode, high priority is given to print speed over print quality. In general, a carriage speed is increased but the head drive frequency is held the same in the draft print mode so that an output image can be produced in a relatively faster time. However, since a dot pitch between adjacent dots becomes greater, the output image is accordingly produced in an inferior print quality.
Therefore, there is presently no ink jet recording apparatus which is capable of increasing a print speed without causing an ink supply shortage to an output image.